The present invention is concerned with a process for the manufacture of ethynyl-.beta.-ionol. Ethynyl-.beta.-ionol is an intermediate used in the preparation of vitamin A.
It has surprisingly been found that ethynyl-.beta.-ionol is obtained in yields of nearly 100%, when .beta.-ionone is reacted with acetylene in the presence of an alkali metal hydroxide in liquid ammonia at a temperature between about -40.degree. and about +30.degree. C.
Conventional alkali metal hydroxides may be employed in the process of this invention with sodium and potassium hydroxide being preferred. Potassium hydroxide is particularly preferred.
A preferred embodiment of the process in accordance with the invention consists in that the reaction is carried out in the temperature range between about -20.degree. and about +5.degree. C., preferably at about 0.degree. C., and at pressures varying from 1.5 atmospheres to 9.5 atmospheres, preferably 8 atmospheres.
The alkali metal hydroxide is generally employed in catalytic amounts varying from about 0.1 mol.% to about 20 mol.%, preferably in an amount of 10 mol.% based on the .beta.-ionone quantity. The alkali metal hydroxide may be employed in larger amounts, i.e., up to 100 mol%, although no significant advantages are gained thereby.
The alkali metal hydroxide is generally used as an aqueous or lower alkanol solution. The term lower alkanol as used herein connotes straight and branched chain alcohols having from 1-6 carbon atoms. The preferred lower alkanoic solution employed herein is a methanolic solution. The concentration of these solutions can vary from about 5 and about 60 wt.%, preferably between about 20 and 50 wt.%, most preferably about 45 wt.%. The alkali metal hydroxide may also be used in solid form, or as a suspension in a suitable liquid.
The process of this invention may be carried out either batchwise or continuously, with the continuous mode being preferred.
After carrying out the reaction, the remaining amount of catalyst is neutralized, for example with a mineral acid or a lower alkanoic acid. Preferred acids that may be employed are sulfuric, nitric, hydrochloric, acetic and the like.